In recent years the market for mobile devices such as mobile phones, PDAs, has grown enormously. The diversity in functionalities and user interfaces has also increased.
Existing mobile devices usually have a display (for example a Liquid Crystal Display) including a cursor which is to be controlled. The control of the cursor on the display is often performed by a 5-way joystick, which contains five switches located under the dome of a knob which can be operated by the user for performing any desired movement of the cursor. By pressing the joystick up or down or to the left or right, one of the four switches is closed, and this causes a corresponding movement of the cursor on the display in steps to a desired direction or position. With this kind of joystick and the use of four of the five switches only control of the cursor in four directions is possible. The fifth switch is usually provided as a central switch and is used for the “click” function, which means that the user can operate a corresponding button associated to the fifth switch to select a certain item on a menu by clicking the knob of the joystick vertically to thereby close the fifth switch.
PDAs and mobile phones nowadays have increasingly larger displays, and the control menus of such devices become more and more complex. Some specific functions such as gaming, web browsing, navigation, etc. may need a more precise and, thus, a continuous control of the cursor rather than a stepped control. The use of touch-screens in smart-phones has been growing enourmously in the past few years. The touch-screen is undoubtedly very handy, intuitive, and user-friendly in many cases. Still, in some cases, such as web-browsing, gaming, and navigation, touch-screens clearly show drawbacks as small items cannot be precisely selected on a web page, or the user's finger covers a part of the screen during gaming or a part of a map in a navigation application. Moreover, the mobile devices in question must be compact, robust, must have low power consumption and also a low price. With a joystick of continuous control (also referred to as an analog joystick) for such a mobile device it should be possible to perform many complicated tasks in the same way as a computer mouse can do, including the press-to-select function (that is, the “click” function), which means that a certain item in the menu can be selected by simply pressing the knob vertically. The analog joystick is seen as a complementary input device to the touch-screen in modern mobile phones and PDAs.
WO 2010/035170 A1 discloses a detection system for the detection of movements of a movable object, said system comprising a light emitting device for emitting light, a reflecting unit being arranged in functional connection with said movable object and being adapted for reflecting said emitted light, a plurality of detectors for detecting said reflected light and outputting detection signals for determining a movement of said movable object, wherein said plurality of detectors includes a first subset of detectors for the detection of a tilt movement of said movable object in a first direction, and a second subset of detectors for the detection of a tilt movement of said movable object in a second direction, and the detection of the tilt movement of said movable object is performed based on a difference in the irradiance of the reflected light on the detectors within each subset of detectors, and wherein said movement of said movable object includes a linear movement in a third direction perpendicular to said first and said second directions and said linear movement of said movable object in said third direction is detected based on the output signals of at least one of the first and the second subsets of detectors. WO 2010/035170 A1 further discloses a corresponding method for detecting movements of a movable object of a detection system. The detection system according to WO 2010/035170 A1, also known as an optical joystick, is able to provide said continuous control of the cursor.
However, the detection system of WO 2010/035170 A1 suffers from the so-called slip-away problem. The slip-away problem means that a target item on a display, i.e. the item that the user wishes to select, is missed just when a click signal is generated. This problem is very annoying for the user.